Detecting watermark modifications

ABSTRACT

Example systems disclosed herein to detect watermark modifications include a watermark encoder to encode a second watermark in a sampled media signal obtained from a received broadcast signal, the sampled media signal already encoded with a first watermark that was included in the received broadcast signal. Disclosed example systems also include a watermark decoder to detect the first watermark and the second watermark in the sampled media signal, and a watermark modification evaluator to compare a first metric determined for the first watermark and a second metric determined for the second watermark to determine whether the first watermark was modified prior to being included in the received broadcast signal. Disclosed example systems further include a ratings server to revise ratings data corresponding to the received broadcast signal when the first watermark is determined to have been modified prior to being included in the received broadcast signal.

RELATED APPLICATION(S)

This patent arises from a continuation of U.S. patent application Ser.No. 15/274,846 (now U.S. Pat. No. 10,102,602), which is entitled“DETECTING WATERMARK MODIFICATIONS” and which was filed on Sep. 23,2016, which claims the benefit of, and priority from, U.S. ProvisionalApplication Ser. No. 62/259,410, which is entitled “DETECTING WATERMARKMODIFICATIONS” and which was filed on Nov. 24, 2015. Priority to U.S.patent application Ser. No. 15/274,846 and U.S. Provisional ApplicationSer. No. 62/259,410 is claimed. U.S. patent application Ser. No.15/274,846 and U.S. Provisional Application Ser. No. 62/259,410 arehereby incorporated by reference herein in their respective entireties.

FIELD OF THE DISCLOSURE

This disclosure relates generally to media watermarking and, moreparticularly, to detecting media watermark modifications.

BACKGROUND

Media watermarking (e.g., such as audio watermarking, videowatermarking, etc.) can be used to identify media, such as televisionbroadcasts, radio broadcasts, advertisements (television and/or radio),downloaded media, streaming media, prepackaged media, etc. Mediawatermarks, such as audio watermarks, are also extensively used in bothradio and television to identify the station or channel to which areceiver is tuned. Existing media watermarking techniques identify mediaby embedding one or more codes (e.g., one or more watermarks) conveyingmedia identifying information and/or an identifier that may be mapped tomedia identifying information, into an audio and/or video component ofthe media. To identify watermarked media, the watermark(s) are extractedand, for example, decoded and/or used to access a table of referencewatermarks that are mapped to media identifying information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example watermark modification detectorimplemented in accordance with the teachings of this disclosure.

FIG. 2 is a table listing example results output from the examplewatermark modification detector of FIG. 1.

FIG. 3 is a flowchart representative of example machine readableinstructions that may be executed to implement the example watermarkmodification detector of FIG. 1.

FIG. 4 is a block diagram of an example processor platform structured toexecute the example machine readable instructions of FIG. 3 to implementthe example watermark modification detector of FIG. 1.

The figures are not to scale. Wherever possible, the same referencenumbers will be used throughout the drawing(s) and accompanying writtendescription to refer to the same or like parts, elements, etc.

DETAILED DESCRIPTION

Methods, apparatus, systems and articles of manufacture (e.g., physicalstorage media) to detect media watermark modifications are disclosed.Example watermark modification detection methods disclosed hereininclude encoding a second watermark in a media signal including a firstwatermark. Disclosed example methods also include detecting the firstwatermark and the second watermark in the media signal. Disclosedexample methods further include, in response to detecting the firstwatermark and the second watermark, comparing a first strength metricdetermined for the first watermark and a second strength metricdetermined for the second watermark to determine whether the firstwatermark was modified prior to being encoded in the media signal.

These and other example methods, apparatus, systems and articles ofmanufacture (e.g., physical storage media) to detect media watermarkmodifications are disclosed in further detail below.

As used herein, the term “media” refers to audio and/or visual (still ormoving) content and/or advertisements. Furthermore, as used herein, theterm “media” includes any type of content and/or advertisement deliveredvia any type of distribution medium. Thus, media includes televisionprogramming or advertisements, radio programming or advertisements,movies, web sites, streaming media, etc.

As noted above, media watermarking (e.g., such as audio watermarking,video watermarking, etc.) is used to identify media, such as televisionbroadcasts, radio broadcasts, advertisements (television and/or radio),downloaded media, streaming media, prepackaged media, etc. Mediawatermarks, such as audio watermarks, are also extensively used in bothradio and television to identify the station or channel to which areceiver is tuned. Existing media watermarking techniques identify mediaby embedding one or more codes (e.g., one or more watermarks) conveyingmedia identifying information and/or an identifier that may be mapped tomedia identifying information, into an audio and/or video component ofthe media. In some examples, the audio or video component is selected tohave a signal characteristic sufficient to hide the watermark. As usedherein, the terms “code” and “watermark” are used interchangeably andare defined to mean any identification information (e.g., an identifier)that may be inserted or embedded in the audio or video of media (e.g., aprogram or advertisement) for the purpose of identifying the media orfor another purpose, such as tuning (e.g., a packet identifying header),copyright protection, etc. In some examples, to identify watermarkedmedia, the watermark(s) are extracted and, for example, decoded and/orused to access a table of reference watermarks that are mapped to mediaidentifying information.

For example, audio watermarks may be embedded at a broadcast facilityand carry digital data in the form of symbols. In a typical application,such as television audience measurement, a metering device installed ina panelist's home senses or otherwise captures audio emanating from, forexample, a television (TV) set and/or other media device(s). Themetering device performs signal processing operations on the audio toextract the watermark symbols representing digital data. In someexamples, the data bits conveyed by the watermark symbols identify theTV station being received by the TV set, and may also represent atimestamp to further identify media (e.g., content and/oradvertisements) being received. In the case of radio audiencemeasurement, as well as in some television audience measurementexamples, the metering device may be a portable device carried by thepanelist to monitor media exposure in the home, as well as in otherenvironments, such as an automobile. Media watermarks designed for radiobroadcasts tend to be more robust than media watermarks designed fortelevision broadcasts because radio broadcasts are often heard inenvironments characterized by relatively high ambient acoustic noise,such as in vehicles. For example, the data packets of media watermarksfor radio broadcasts may be repeated multiple times to provideredundancy.

In the case of radio audience measurement, a widely used watermark isthe Critical Band Encoding Technology (CBET) watermark invented byJensen, et al. See U.S. Pat. Nos. 5,450,490 and 5,764,763. See also U.S.Pat. Nos. 6,845,360 and 6,871,180. In CBET watermarking, each datapacket includes 32 bits of which 16 bits are used for stationidentification and the remaining 16 bits are used for a timestamp. CBETwatermarking can also be used for television audience measurement.

CBET watermarks are constructed using symbols representing 4 bits ofdata. Each symbol is encoded in 400 milliseconds of host audio and iscreated by embedding a particular set of 10 tones representing eachsymbol, with different sets of tones being used to represent differentsymbol values. Each tone belongs to a “code band” consisting of severalclosely spaced frequencies of the audio. The code tones are in thefrequency range 1 kHz to 3 kHz in the case of CBET watermarking.

In some examples, to make these code tones imperceptible to the humanear, the amplitude of each of the tones is controlled by a “masking”energy offered by the host audio in a set of frequency bands (“codebands”) in which these tones reside. Host audio that is rich in spectralenergy in these code bands will support higher code tone amplitudes dueto psycho-acoustic perception characteristics of the human ear. However,the masking characteristics do not remain constant across a 400millisecond block of audio. In some examples, the maskingcharacteristics are recalculated frequently at intervals as short as 2milliseconds.

Even with the resulting amplitude modulation of the code tones, the codetones can be successfully detected by signal processing techniques usedfor watermark detection, such as a Discrete Fourier Transform (DFT)performed on an audio block of 256 milliseconds lying anywhere withinthe 400-millisecond block of audio to determine the respective energiesof the different frequencies, or tones, included in the audio. Each ofthe code tones included in the watermark symbol will tend to havesignificantly higher energy than other members of the code bandassociated with that tone. In some watermark detection procedures, theenergy of each potential code tone of the audio is normalized relativeto (e.g., divided by) the average energy in its code band. By adding thenormalized energy of the set of code tones (e.g., all the 10 tones)representing a symbol, a strength metric (or, in other words, a strengthvalue) for the symbol may be determined. A winning symbol, representingthe decoded watermark symbol, may be selected by comparing the strengthmetrics of all potential symbols and selecting the winning symbol to bethe potential symbol with the largest strength metric. In some examples,the winning symbol is considered valid if its strength metric exceeds athreshold.

Thus, in some examples, the CBET watermark detection process performedin a metering device involves analyzing a block of audio samplescorresponding to 256 milliseconds to determine the presence of a validCBET symbol. In general, the 400 millisecond symbol block boundaries arenot known to the decoding process operating in the meter. Therefore ascan operation consisting of sliding a 256 millisecond window across theaudio stream is performed. This is usually performed in slidingincrements that could be as large as 100 milliseconds.

In some examples, an audio component of media (also referred to as thehost audio) can carry multiple watermarks, which overlap in time, usingfrequency multiplexing. For example, CBET watermarking supports 4“layers” in which each layer uses distinct sets of code tones torepresent its associated symbols (e.g., with different layers usingdifferent sets of code tones). In some examples of CBET watermarking forradio, just one of these layers, which is called the “local” layer, isused for encoding watermarks. In some examples of CBET watermarking fortelevision, such as examples in which networks deliver programs to localaffiliates, two (2) layers of watermarking, called the “network” layerand the “local” layer, are used for encoding watermarks.

In radio audience measurement scenarios in which much of the listeningoccurs in a high ambient noise environment, such as a moving automobile,the energy of the embedded watermark tones is an important factor in thesuccessful detection of the watermarks. Spectrally rich content, such asmusic, typically contains more masking energy across the 10 code bandsrelative to content consisting of speech. To allow for these variations,the watermarks are generally repeated multiple times. For example, theCBET watermark message consists of 12 symbols and the total duration is12×0.4=4.8 seconds. In some such examples, the same watermark message,including station identification and timestamp, is repeated for anentire minute of audio. The detection process takes advantage of thisredundancy, namely, every 400 millisecond block that is separated intime by 4.8 seconds is likely to carry the same symbol or, in otherwords, the same set of 10 tones. The watermark symbol tone energies canbe summed across blocks separated by 4.8 seconds to yield asignificantly more robust watermark decoding result. Thus, in some suchexamples, even spectrally weak content, such as speech, yields a fewdetections every minute.

Recently, watermark boosting devices, such as the VOLTAIR® device, thatboost CBET code tones at the broadcast facility have been introduced.These devices perform a training procedure in which the differencesbetween the input and output signals of a CBET watermark encoder aredetermined by buffering and analyzing samples of audio input to the CBETwatermark encoder as well as the samples produced at the output of theCBET watermark encoder. The resulting differences determined by thetraining procedure yield the 10 frequency tones associated with awatermark symbol, along with their current amplitude. The watermarkboosting devices then increase the amplitudes of the watermark symbolcode tones by using more aggressive psycho-acoustic models, especiallyif longer buffers than those employed by the CBET encoder are used. Therecomputed or enhanced code tones are added to the original input andsent as the watermarked audio output to generate a new watermarkedversion of the audio with potential higher detection rates. Somewatermark boosting devices have settings that allow an operator tochoose boost values in the range from 0 to 25. However, such watermarkboosting can lead to audible artifacts that corrupt the host audio.

Thus, there is a need to be able to detect whether watermarks embeddedin media signals have been artificially boosted, which can lead toskewed detection rates, corrupted audio, etc. Turning to the figures, ablock diagram of an example watermark modification detector 100implemented in accordance with the teachings of this disclosure isillustrated in FIG. 1. The watermark modification detector 100 of theillustrated example examines watermarked media (e.g., watermarked audio)to passively detect the presence of watermark boosting and, byextension, whether a watermark boosting device is being employed by amedia source (e.g., a radio or television station).

In the illustrated example of FIG. 1, the watermark modificationdetector 100 includes an example media signal sampler 105 to capture asample of a media signal, such as an audio signal, output from, forexample, an example media device 110 tuned to a radio station or atelevision station to be examined. For example, the media signal sampler105 may include a microphone and/or a line input to capture 10 minutes,or some other duration, of audio output from the media device 110. Theexample media device 110 may be implemented by any media device, such asa radio, a television, a computer, a smartphone, a tablet, etc. In thefollowing description, the media signal sampled and processed by thewatermark modification detector 100 is assumed to be an audio signal.However, in other examples, the media signal sampled and processed bythe watermark modification detector 100 could be a video signal and/orsome other media signal output by the media device 110.

The example watermark modification detector 100 also includes an examplewatermark encoder 115 to encode a watermark into an unused watermarkinglayer in the audio signal sampled by the media signal sampler 105. Asdescribed above, multiple layers of watermarking can co-exist due tofrequency multiplexing. For example, as noted above, CBET watermarkencoders for radio stations use a first layer, namely, the “local” layerfor inserting CBET watermarks. Thus, in some such examples, thewatermark encoder 115 implements a CBET watermark encoded to encode awatermark into the captured audio using a second layer, namely, the“network” layer supported the CBET encoder. As another example, and asnoted above, CBET watermark encoders for television stations may use afirst layer, namely, the “local” layer, and a second layer, namely, the“network” layer for inserting CBET watermarks. Thus, in some suchexamples, the watermark encoder 115 encodes a watermark into thecaptured audio using a third unused layer of the four possiblewatermarking layers. In general, if the audio signal sampled by themedia signal sampler 105 can include a first (e.g., original) watermarkin a first one of the watermarking layers, the watermark encoder 115encodes a second (e.g., added) watermark in a second (e.g., unused) oneof the watermarking layers.

The example watermark modification detector 100 further includes anexample watermark decoder 120 to analyze the sampled audio encoded bythe watermark encoder 115 with the additional watermark in the unusedwatermarking layer. In some examples, the watermark decoder 120 isimplemented by a modified CBET watermark decoder, which performs asliding 256-millisecond DFT block analysis, as described above, todetect CBET watermark symbols. For each detected symbol, if it is valid(e.g., if its detected sum of normalized code tone energies exceeds athreshold), the symbol's strength metric (e.g., the value of the sum ofnormalized code tone energies for the symbol) is stored in an array. Insome examples, separate arrays are used for the original watermarksymbols (e.g., the “local” layer symbols in the case of radiowatermarking) and the added watermark symbols encoded by the watermarkencoder 115 (e.g., the “network” layer symbols in the case of radiowatermarking).

In the illustrated example, the watermark decoder 120 outputs thedecoded watermark symbols via an example symbol output 125 and thesymbol strength metrics for the decoded symbols via an example strengthoutput 130. These outputs are provided to an example watermarkmodification evaluator 135 included in the example watermarkmodification detector 100, which compares the strength metrics for theoriginal watermark symbols (e.g., the “local” layer symbols in the caseof radio watermarking) and the strength metrics for the added watermarksymbols encoded by the watermark encoder 115 (e.g., the “network” layersymbols in the case of radio watermarking) to determine whether theoriginal watermark symbols underwent boosting by a watermark boostingdevice prior to being encoded in the audio signal. For example, when itsanalysis of the 10 minutes of captured audio is completed, the watermarkdecoder 120 outputs strength metrics for the original watermark symbolsand the added watermark symbols detected during that analysis interval.The example watermark modification evaluator 135 then combines (e.g.,averages) the strength metrics for the original watermark symbols todetermine a combined (e.g., average) symbol strength metric for theoriginal watermark symbols (e.g., the local layer symbols). Thewatermark modification evaluator 135 of the illustrated example alsocombines (e.g., averages) the strength metrics for the added watermarksymbols to determine a combined (e.g., average) symbol strength metricfor the added watermark symbols (e.g., the network layer symbols).

Next, the example watermark modification evaluator 135 compares thecombined (e.g., average) symbol strength metric for the added watermarksymbols with the combined (e.g., average) symbol strength metric for theoriginal watermark symbols. The combined (e.g., average) symbolstrengths of the added (e.g., “network” layer) watermark and theoriginal (e.g., “local” layer) watermark should, under normalcircumstances, be approximately the same because the host audio'smasking capability computed by the watermark encoder 115 when encodingthe added watermark symbols should be the same as, or at least similarto, the host audio's masking capability computed by the watermarkencoder that encoded the original watermark symbols. However, if a moreaggressive masking model is employed by the original watermark encoder,as in the case of the watermark boosting devices described above, thecombined (e.g., average) symbol strength for the original watermarksymbols will typically be larger than the combined (e.g., average)symbol strength metric for the added watermark symbols. Thus, if thecombined (e.g., average) symbol strength for the original (e.g., locallayer) watermark symbols is less than or equal to, or just slightlyhigher than (e.g., within a threshold amount of) the combined (e.g.,average) symbol strength metric for the added (e.g., network layer)watermark symbols, the watermark modification evaluator 135 indicates orotherwise determines that the original watermark did not undergoboosting and, thus, no watermark boosting device (or other enhancementdevice) is in operation at the media source (e.g., radio or televisionstation). Otherwise, if the combined (e.g., average) symbol strength forthe original (e.g., local layer) watermark symbols is greater than(e.g., by a threshold amount of) the combined (e.g., average) symbolstrength metric for the added (e.g., network layer) watermark symbols,the watermark modification evaluator 135 indicates or otherwisedetermines that the original watermark did undergo boosting and, thus, awatermark boosting device (or other enhancement device) is in operationat the media source (e.g., radio or television station).

In the illustrated example, the watermark modification evaluator 135reports a watermark modification report including its determination asto whether a watermarked media signal has undergone boosting to anaudience measurement entity (AME) 140, such as The Nielsen Company (US),LLC. For example, the watermark modification evaluator 135 may transmitits watermark modification report to the AME 140 via an example network145. The example network 145 may correspond to the Internet and/or anyother communication network or combination of networks. In someexamples, a ratings server and/or other computing device at the AME 140receives the report (or message, signal, etc.) indicating whether thewatermarked media signal has undergone boosting and uses thatinformation to, for example, adjust or discard ratings data determinedfor media, a station, a source, etc., corresponding to the watermarkedmedia signal.

An example watermark modification report 200 capable of being output bythe example watermark modification detector 100 is represented by thetable illustrated in FIG. 2. The example watermark modification report200 includes an example station column 205 to identify the radio and/ornetwork station whose media signals were analyzed by the watermarkmodification detector 100 to determine whether the watermarks encoded inthe broadcast media signals have been modified (e.g., boosted orotherwise enhanced). The example watermark modification report 200 alsoincludes an example network average symbol strength column 210 to listthe average symbol strength metrics computed for the added (e.g.,network layer) watermark symbols encoded into a station's media signalby the watermark modification detector 100. The example watermarkmodification report 200 further includes an example local average symbolstrength column 215 to list the average symbol strength metrics computedfor the original (e.g., local layer) watermark symbols originallyencoded into a station's media signal prior to analysis by the watermarkmodification detector 100. The example watermark modification report 200includes an example modification evaluation column 220 to list thedetermination made by the watermark modification detector 100 as towhether the original watermark symbols encoded into a station's mediasignal have undergone modification (e.g., boosting or otherenhancement).

In the illustrated example of FIG. 2, the watermark modification report200 includes six (6) example rows 225-250 providing the results for six(6) example stations, Station 1 through Station 6. In the illustratedexample of FIG. 2, the watermark modification detector 100 uses athreshold of four (4) to determine whether the original watermarksymbols encoded into a station's media signal have undergonemodification (e.g., boosting or other enhancement). Thus, in the examplewatermark modification report 200 of FIG. 2, the modification evaluationcolumn 220 indicates that the watermark modification detector 100determined that the media signals for Station 1, Station 2 and Station 3underwent watermark enhancement (e.g., boosting), because, for each ofthese stations, the average symbol strength metric computed for theoriginal (e.g., local layer) watermark symbols is greater than theaverage symbol strength metric computed for the added (e.g., networklayer) watermark symbols by at least the threshold amount (e.g., 4 inthis example). Conversely, in the example watermark modification report200 of FIG. 2, the modification evaluation column 220 indicates that thewatermark modification detector 100 determined that the media signalsfor Station 4, Station 5 and Station 6 did not undergo watermarkenhancement (e.g., boosting), because, for each of these stations, theaverage symbol strength metric computed for the original (e.g., locallayer) watermark symbols was not greater than the average symbolstrength metric computed for the added (e.g., network layer) watermarksymbols by at least the threshold amount (e.g., 4 in this example).

While an example manner of implementing the example watermarkmodification detector 100 is illustrated in FIG. 1, one or more of theelements, processes and/or devices illustrated in FIG. 1 may becombined, divided, re-arranged, omitted, eliminated and/or implementedin any other way. Further, the example media signal sampler 105, theexample watermark encoder 115, the example watermark decoder 120, theexample watermark modification evaluator 135 and/or, more generally, theexample watermark modification detector 100 of FIG. 1 may be implementedby hardware, software, firmware and/or any combination of hardware,software and/or firmware. Thus, for example, any of the example mediasignal sampler 105, the example watermark encoder 115, the examplewatermark decoder 120, the example watermark modification evaluator 135and/or, more generally, the example watermark modification detector 100could be implemented by one or more analog or digital circuit(s), logiccircuits, programmable processor(s), application specific integratedcircuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or fieldprogrammable logic device(s) (FPLD(s)). When reading any of theapparatus or system claims of this patent to cover a purely softwareand/or firmware implementation, at least one of the example watermarkmodification detector 100, the example media signal sampler 105, theexample watermark encoder 115, the example watermark decoder 120 and/orthe example watermark modification evaluator 135 is/are hereby expresslydefined to include a tangible computer readable storage device orstorage disk such as a memory, a digital versatile disk (DVD), a compactdisk (CD), a Blu-ray disk, etc. storing the software and/or firmware.Further still, the example watermark modification detector 100 mayinclude one or more elements, processes and/or devices in addition to,or instead of, those illustrated in FIG. 1, and/or may include more thanone of any or all of the illustrated elements, processes and devices.

A flowchart representative of example machine readable instructions forimplementing the example watermark modification detector 100, theexample media signal sampler 105, the example watermark encoder 115, theexample watermark decoder 120 and/or the example watermark modificationevaluator 135 is shown in FIG. 3. In this example, the machine readableinstructions comprise one or more programs for execution by a processor,such as the processor 412 shown in the example processor platform 400discussed below in connection with FIG. 4. The one or more programs, orportion(s) thereof, may be embodied in software stored on a tangiblecomputer readable storage medium such as a CD-ROM, a floppy disk, a harddrive, a digital versatile disk (DVD), a Blu-ray Disk™, or a memoryassociated with the processor 412, but the entire program or programsand/or portions thereof could alternatively be executed by a deviceother than the processor 412 and/or embodied in firmware or dedicatedhardware (e.g., implemented by an ASIC, a PLD, an FPLD, discrete logic,etc.). Further, although the example program(s) is(are) described withreference to the flowchart illustrated in FIG. 3, many other methods ofimplementing the example watermark modification detector 100, theexample media signal sampler 105, the example watermark encoder 115, theexample watermark decoder 120 and/or the example watermark modificationevaluator 135 may alternatively be used. For example, with reference tothe flowchart illustrated in FIG. 3, the order of execution of theblocks may be changed, and/or some of the blocks described may bechanged, eliminated, combined and/or subdivided into multiple blocks.

As mentioned above, the example process of FIG. 3 may be implementedusing coded instructions (e.g., computer and/or machine readableinstructions) stored on a tangible computer readable storage medium suchas a hard disk drive, a flash memory, a read-only memory (ROM), acompact disk (CD), a digital versatile disk (DVD), a cache, arandom-access memory (RAM) and/or any other storage device or storagedisk in which information is stored for any duration (e.g., for extendedtime periods, permanently, for brief instances, for temporarilybuffering, and/or for caching of the information). As used herein, theterm tangible computer readable storage medium is expressly defined toinclude any type of computer readable storage device and/or storage diskand to exclude propagating signals and to exclude transmission media. Asused herein, “tangible computer readable storage medium” and “tangiblemachine readable storage medium” are used interchangeably. Additionallyor alternatively, the example process of FIG. 3 may be implemented usingcoded instructions (e.g., computer and/or machine readable instructions)stored on a non-transitory computer and/or machine readable medium suchas a hard disk drive, a flash memory, a ROM, a CD, a DVD, a cache, a RAMand/or any other storage device or storage disk in which information isstored for any duration (e.g., for extended time periods, permanently,for brief instances, for temporarily buffering, and/or for caching ofthe information). As used herein, the term non-transitory computerreadable medium is expressly defined to include any type of computerreadable storage device and/or storage disk and to exclude propagatingsignals and to exclude transmission media. As used herein, when thephrase “at least” is used as the transition term in a preamble of aclaim, it is open-ended in the same manner as the terms “comprising” and“including” are open ended. Also, as used herein, the terms “computerreadable” and “machine readable” are considered equivalent unlessindicated otherwise.

An example program 300 that may be executed to implement the examplewatermark modification detector 100 of FIG. 1 is illustrated in FIG. 3.With reference to the preceding figures and associated writtendescriptions, the example program 300 of FIG. 3 begins execution atblock 305 at which the example media signal sampler 105 of the watermarkmodification detector 100 samples a media signal, which may include afirst (e.g., original) watermark (e.g., a local watermark) associatedwith a first watermarking level (e.g., a local level), output from theexample media device 110, as described above. At block 310, the examplewatermark encoder 115 of the watermark modification detector 100 encodesa second (e.g., added) watermark (e.g., a network watermark) associatedwith a second watermarking level (e.g., a network level) in the samplemedia signal, as described above. At block 315, the example watermarkdecoder 120 of the watermark modification detector 100 performs awatermark detection procedure, as described above, to detect the first(e.g., original) and second (e.g., added) watermarks encoded in themedia signal, as described above. If the watermark decoder 120 does notdetect both types of watermarks (block 320), processing proceeds toblock 325 at which the watermark modification detector 100 indicates(e.g., via an output/transmitted report, message, signal, etc.) that itwas not possible to determine whether the first (e.g., original)watermark associated was modified (e.g., boosted or otherwise enhanced)at the media source (e.g., radio or television station) after originallybeing encoded in the media signal.

However, if the watermark decoder 120 does detect both types ofwatermarks (block 320), at block 330, the example watermark modificationevaluator 135 of the watermark modification detector 100 determines acombined (e.g., average) symbol strength metric for the first (e.g.,original) watermark symbols, as described above. At block 335, theexample watermark modification evaluator 135 determines a combined(e.g., average) symbol strength metric for the second (e.g., added)watermark symbols, as described above. If the symbol strength metric forthe first (e.g., original) watermark symbols is greater than the symbolstrength metric for the second (e.g., added) watermark symbols (block340) by a threshold amount, then at block 345, the watermarkmodification evaluator 135 indicates, as described above, that watermarkmodification (e.g., boosting or other enhancement) has been detected.However, if the symbol strength metric for the first (e.g., original)watermark symbols is not greater than the symbol strength metric for thesecond (e.g., added) watermark symbols (block 340) by the thresholdamount, then at block 350, the watermark modification evaluator 135indicates, as described above, that watermark modification (e.g.,boosting or other enhancement) has not been detected. At block 355, thewatermark modification evaluator 135 reports, as described above, thewatermark modification determinations made at block 345 or block 350.Execution of the example program 300 then ends.

FIG. 4 is a block diagram of an example processor platform 400structured to execute the instructions of FIG. 3 to implement theexample watermark modification detector 100 of FIG. 1. The processorplatform 400 can be, for example, a server, a personal computer, amobile device (e.g., a cell phone, a smart phone, a tablet such as aniPad™), or any other type of computing device.

The processor platform 400 of the illustrated example includes aprocessor 412. The processor 412 of the illustrated example is hardware.For example, the processor 412 can be implemented by one or moreintegrated circuits, logic circuits, microprocessors or controllers fromany desired family or manufacturer. In the illustrated example of FIG.4, the processor 412 includes one or more example processing cores 415configured via example instructions 432, which include the exampleinstructions of FIG. 3, to implement the example media signal sampler105, the example watermark encoder 115, the example watermark decoder120 and/or the example watermark modification evaluator 135 of FIG. 1.

The processor 412 of the illustrated example includes a local memory 413(e.g., a cache). The processor 412 of the illustrated example is incommunication with a main memory including a volatile memory 414 and anon-volatile memory 416 via a link 418. The link 418 may be implementedby a bus, one or more point-to-point connections, etc., or a combinationthereof. The volatile memory 414 may be implemented by SynchronousDynamic Random Access Memory (SDRAM), Dynamic Random Access Memory(DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any othertype of random access memory device. The non-volatile memory 416 may beimplemented by flash memory and/or any other desired type of memorydevice. Access to the main memory 414, 416 is controlled by a memorycontroller.

The processor platform 400 of the illustrated example also includes aninterface circuit 420. The interface circuit 420 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 422 are connectedto the interface circuit 420. The input device(s) 422 permit(s) a userto enter data and commands into the processor 412. The input device(s)can be implemented by, for example, an audio sensor, a microphone, acamera (still or video), a keyboard, a button, a mouse, a touchscreen, atrack-pad, a trackball, a trackbar (such as an isopoint), a voicerecognition system and/or any other human-machine interface. Also, manysystems, such as the processor platform 400, can allow the user tocontrol the computer system and provide data to the computer usingphysical gestures, such as, but not limited to, hand or body movements,facial expressions, and face recognition.

One or more output devices 424 are also connected to the interfacecircuit 420 of the illustrated example. The output devices 424 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay, a cathode ray tube display (CRT), a touchscreen, a tactileoutput device, a printer and/or speakers). The interface circuit 420 ofthe illustrated example, thus, typically includes a graphics drivercard, a graphics driver chip or a graphics driver processor.

The interface circuit 420 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodem and/or network interface card to facilitate exchange of data withexternal machines (e.g., computing devices of any kind) via a network426 (e.g., an Ethernet connection, a digital subscriber line (DSL), atelephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 400 of the illustrated example also includes oneor more mass storage devices 428 for storing software and/or data.Examples of such mass storage devices 428 include floppy disk drives,hard drive disks, compact disk drives, Blu-ray disk drives, RAID(redundant array of independent disks) systems, and digital versatiledisk (DVD) drives.

Coded instructions 432 corresponding to the instructions of FIG. 3 maybe stored in the mass storage device 428, in the volatile memory 414, inthe non-volatile memory 416, in the local memory 413 and/or on aremovable tangible computer readable storage medium, such as a CD or DVD436.

Further implementation details concerning example methods, apparatus,systems and articles of manufacture (e.g., physical storage media) todetect media watermark modifications in accordance with the teachings ofthis disclosure are provided in the Appendix.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent.

What is claimed is:
 1. A system to detect watermark modifications, thesystem comprising: a watermark encoder to encode a second watermark in asampled media signal obtained from a received broadcast signal, thesampled media signal already encoded with a first watermark that wasincluded in the received broadcast signal; a watermark decoder to detectthe first watermark and the second watermark in the sampled mediasignal; a watermark modification evaluator to compare a first metricdetermined for the first watermark and a second metric determined forthe second watermark to determine whether the first watermark wasmodified prior to being included in the received broadcast signal; and aratings server to revise ratings data corresponding to the receivedbroadcast signal when the first watermark is determined to have beenmodified prior to being included in the received broadcast signal. 2.The system of claim 1, wherein the ratings server is to discard theratings data when the first watermark is determined to have beenmodified prior to being included in the received broadcast.
 3. Thesystem of claim 1, wherein the received broadcast signal is a receivedradio station signal, and the sampled media signal is a sampled audiosignal obtained from the received radio station signal.
 4. The system ofclaim 1, wherein the first metric is a first signal strength metricdetermined for the first watermark and the second metric is a secondsignal strength metric determined for the second watermark.
 5. Thesystem of claim 4, wherein the watermark modification evaluator is to:determine the first watermark was modified prior to being included inthe received broadcast when the first signal strength metric exceeds thesecond signal strength metric by at least a threshold amount; anddetermine the first watermark was not modified prior to being includedin the received broadcast when the first signal strength metric does notexceed the second signal strength metric by at least a threshold amount.6. The system of claim 1, wherein the watermark encoder is to encode thesecond watermark to overlap in time with the first watermark in thesampled media signal.
 7. The system of claim 6, wherein the watermarkencoder is to employ frequency multiplexing to encode the secondwatermark to overlap in time with the first watermark in the sampledmedia signal.
 8. A non-transitory computer readable medium comprisingcomputer readable instructions that, when executed, cause a processor toat least: encode a second watermark in a sampled media signal obtainedfrom a received broadcast signal, the sampled media signal alreadyencoded with a first watermark that was included in the receivedbroadcast signal; detect the first watermark and the second watermark inthe sampled media signal; compare a first metric determined for thefirst watermark and a second metric determined for the second watermarkto determine whether the first watermark was modified prior to beingincluded in the received broadcast signal; and revise ratings datacorresponding to the received broadcast signal when the first watermarkis determined to have been modified prior to being included in thereceived broadcast signal.
 9. The computer readable medium of claim 8,wherein the instructions, when executed, cause the processor to discardthe ratings data when the first watermark is determined to have beenmodified prior to being included in the received broadcast.
 10. Thecomputer readable medium of claim 8, wherein the received broadcastsignal is a received radio station signal, and the sampled media signalis a sampled audio signal obtained from the received radio stationsignal.
 11. The computer readable medium of claim 8, wherein the firstmetric is a first signal strength metric determined for the firstwatermark and the second metric is a second signal strength metricdetermined for the second watermark.
 12. The computer readable medium ofclaim 11, wherein the instructions, when executed, cause the processorto: determine the first watermark was modified prior to being includedin the received broadcast when the first signal strength metric exceedsthe second signal strength metric by at least a threshold amount; anddetermine the first watermark was not modified prior to being includedin the received broadcast when the first signal strength metric does notexceed the second signal strength metric by at least a threshold amount.13. The computer readable medium of claim 8, wherein the instructions,when executed, cause the processor to encode the second watermark tooverlap in time with the first watermark in the sampled media signal.14. The computer readable medium of claim 13, wherein the instructions,when executed, cause the processor employ frequency multiplexing toencode the second watermark to overlap in time with the first watermarkin the sampled media signal.
 15. A watermark modification detectorcomprising: means for encoding a second watermark in a sampled mediasignal obtained from a broadcast media signal received by a mediadevice, the sampled media signal including a first watermark that wasincluded in the broadcast media signal; means for detecting the firstwatermark and the second watermark in the sampled media signal; andmeans for comparing a first strength metric determined for the firstwatermark and a second strength metric determined for the secondwatermark to determine whether the first watermark was modified prior tobeing encoded in the broadcast media signal that was received by themedia device.
 16. The watermark modification detector of claim 15,wherein the first watermark is encoded in a first watermarking layer ofthe sampled media signal, and the watermark encoder is to encode thesecond watermark in a second watermarking layer of the sampled mediasignal.
 17. The watermark modification detector of claim 15, wherein themeans for detecting is to: sum energies of respective ones of a firstset of code tones of the sampled media signal corresponding to symbolsof the first watermark to determine the first strength metric; and sumenergies of respective ones of a second set of code tones of the sampledmedia signal corresponding to symbols of the second watermark todetermine the second strength metric.
 18. The watermark modificationdetector of claim 17, wherein the means for detecting is to: normalizethe respective energy of one of the first set of code tones based on afirst average energy determined for a first code band of the sampledmedia signal including the one of the first set of code tones; andnormalize the respective energy of one of the second set of code tonesbased on a second average energy determined for a second code band ofthe sampled media signal including the one of the second set of codetones.
 19. The watermark modification detector of claim 15, wherein themeans for comparing is to determine whether the second strength metricfor the second watermark exceeds the first strength metric for the firstwatermark by at least a threshold value.
 20. The watermark modificationdetector of claim 19, wherein the means for comparing is to: determinethe first watermark was modified prior to being encoded in the broadcastmedia signal when the second strength metric exceeds the first strengthmetric by at least the threshold value; determine the first watermarkwas not modified prior to being encoded in the broadcast media signalwhen the second strength metric does not exceed the first strengthmetric by at least the threshold value; and report, via a network,information indicating whether the first watermark was modified prior tobeing encoded in the broadcast media signal.